[AAVSO-HEN] Transient in NGC2770 / SN2008D: Metallicity of nearby HII regions

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
For an archive and more information on circulars visit:
http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3_archive.html

TITLE:   GCN CIRCULAR
NUMBER:  7192
SUBJECT: Transient in NGC2770 / SN2008D: Metallicity of nearby HII regions 
DATE:    08/01/17 15:27:09 GMT
FROM:    Edo Berger at Princton U  <eberger at astro.princeton.edu>

E. Berger and A. M. Soderberg (Princeton) report on behalf of a larger 
collaboration:

"We used the ARC 3.5-m telescope at Apache Point Observatory to obtain 
spectroscopic observations of the X-ray transient in NGC2770 (GCN 7159). 
We obtained 4x1200 sec exposures with the DIS red+blue cameras providing a 
wavelength range of 3600-9000A.  The spectra therefore cover a wide range 
of nebular emission lines relevant for metallicity measurements (i.e. 
[OII], H-beta, [OIII], H-alpha, [NII], and [SII]).  Following the 
prescriptions of Kewley & Dopita (2002) we use several indicators (e.g. 
[NII]/[OII], R23) to measure the metallicity and ionization parameter of 
bright HII regions within +/-8 arcsec (about 1 kpc) of the X-ray transient 
position.  We find metallicities of 12+log(O/H)=8.9+/-0.2, or about 
0.6-1.6 times the solar metallicity.  The error bar includes both the 
spread in metallicity and the systematic uncertainty between the various 
indicators.  This value is higher, and more robust, than the estimate in 
GCN 7189 which relied on an assumed metallicity gradient."